whereas picking a target level of saltiness in your dish and optimizing might work just fine.

The point is that you optimize for taste and let saltiness fall where it may. Similarly, LW should optimize for some metric of "goodness" and let negative karma be whatever it has to be to produce that deliciousness.

Of course. But that may be ill-specified and hard to measure, and something else may be a usable proxy.

Your (perfectly correct) point is that optimizing a poorly chosen proxy (e.g., minimizing the amount of salt) can produce very poor results. My point is that even if you have what looks like an excellently chosen proxy, as soon as you start optimizing it your (or others') ingenuity is liable to turn up ways to improve it while making what you care about worse.

(None the less, proxy measurements are really useful. I believe we are agreed that at the very least they're worth keeping an eye on as a rough guide, provided you also keep an eye on whether they're ceasing to be useful proxies.)